Electronically commutatable motor comprising an electronic control unit

ABSTRACT

An electronically commutatable motor is disclosed, whose field windings are controllable via electronic control unit using PWM control signals via semiconductor output stages, a setpoint being selectable for the control unit and the control unit outputting corresponding PWM control signals to the semiconductor output stages. In order to recognize malfunctions which could result in overload of the motor and the electronic components thereof even in the acceleration phase and to be capable of using this to protect against overload, after selection of the setpoint and/or switching on of the control unit and/or the semiconductor output stages, the control unit outputs ramp-type speed-increasing PWM control signals to the semiconductor output stages during a selected or selectable acceleration time until the final control of the semiconductor output stages corresponding to the setpoint is reached, during the acceleration time a setpoint speed corresponding to the PWM control signals may be compared with the detected actual speed of the motor, and, in the event of deviations of the actual speed from the setpoint speed by a selected or selectable speed deviation, the control unit and/or the semiconductor output stages may be switched off.

FIELD OF THE INVENTION

The present invention relates to an electronically commutatable motor,whose field windings are controllable by an electronic control unit viasemiconductor output stages using PWM control signals, a nominalsetpoint speed being selectable for the control unit and the actualspeed being comparable with the setpoint, and when the actual speeddeviates from the setpoint by a selected or selectable speed difference,the control unit and/or the semiconductor output stages are capable ofbeing switched off.

BACKGROUND INFORMATION

An electronically commutatable motor is discussed in U.S. Pat. No.5,744,921. This motor is operable at different nominal operating speeds,the setpoint applied determining the PWM control signals and theassociated nominal operating speed. Each operating state may bemonitored by comparison and deviation between the actual speed and anassociated setpoint speed. The motor may be switched off when the speedsdiffer by a selected speed deviation. In this motor, the control unitmay be capable of modifying the PWM control signals so that the motorruns in the correct direction of rotation for the operating state as afunction of the rest position of the rotor.

The motor may be switched off in the event of a speed deviation from thesetpoint by a selected value, as discussed in Japanese Patent No. 10 322894, where the motor may be switched off by switching off the supplyvoltage, as discussed in German Published Patent Application No. 43 30823.

These types of electronically commutatable motors may be used forvarious applications. In this regard, it may happen that even theacceleration of the motor to a desired nominal operating speed, which isselectable or selected via a setpoint, does not occur in the correctway. The motor may be capable of stalling in the rest position orprevented from accelerating correctly by an excessive load or otherimpediments. Mechanical defects may also cause such a phenomenon. Themotor may also block in any phase of the acceleration. The motor and/orits electronic components may be overloaded and even damaged.

It is the object of the present invention to monitor and switch off anelectronically commutatable motor of the type initially described,during each phase of the acceleration in such a way that an overload ordamage to the motor is prevented as early as in this acceleration phase,rather than in the desired operating state.

SUMMARY OF THE INVENTION

In an exemplary embodiment of the present invention, with the selectionof the setpoint and/or switching on the control unit and/or thesemiconductor output stages as a function of the selected setpoint, thecontrol unit determines a corresponding acceleration time in which thePWM control signals, which gradually increase the speed, increase to afinal value associated with the selected setpoint. In the control unit asetpoint speed is associated with each control value of the PWM controlsignals. In each control phase of the acceleration time, the actualspeed is measured and compared with the setpoint speed associated withthe corresponding PWM control signal. Switch-off occurs as early asduring acceleration if in a control phase the measured actual speeddeviates by the selected speed difference from the setpoint speedassociated with the corresponding PWM control signal.

The acceleration phase is divided into time segments by the graduallyincreasing PWM control signals; in each case the coincidence of theactual speed with the setpoint (i.e., the PWM control signal beingapplied) also corresponds to the motor characteristic and indicatesundistrubed acceleration of the motor. If a deviation from a permissiblespeed deviation occurs in a time segment of the acceleration phase, amechanical or electric malfunction may be present, which may justify themotor being switched off in order to protect the motor or its componentsfrom overload and damage.

In this manner, the entire acceleration phase may be monitored forcorrect start and acceleration from the time the motor is switched on.

The PWM control signals which gradually increase the speed maycontinuously increase in pulse amplitude, pulse width, and/orcommutating frequency.

The actual speed may be compared to the setpoint speed continuously orrepeatedly at time intervals during the acceleration.

The simple protective circuit may be obtained by switching the controlunit and/or the semiconductor output stages on and off by switching thesupply voltage on and off.

For different operating modes, the design may advantageously be suchthat the acceleration time depends on the magnitude of the selectablesetpoint and/or on the magnitude of the supply voltage.

The variation of the permissible speed deviation may be designed so thatthe selected speed deviation depends on the selected setpoint and/or onthe magnitude of the supply voltage.

If necessary, the deviation from the selected speed deviation may bevisually displayed and/or acoustically indicated.

The comparison device required to compare actual speed and setpointspeed may be integrated into the control unit.

For the duration of the operation of the motor with the operating speeddefined by the selected setpoint, the comparison between actual andsetpoint speed may be continued to obtain overload protection also inthis phase of the steady-state operation and be capable of switching offif necessary.

BRIEF DESCRIPTION OF THE DRAWING

The FIGURE illustrates schematically an exemplary embodiment of thepresent invention.

DETAILED DESCRIPTION

The motor unit may include the following functional units: control unitSTE, semiconductor output stages EST, and actual motor M having thefield windings of the stator and the permanent magnet rotor, which maybe designed as an external or internal rotor.

If motor M is to be put into operation, a setpoint N_(setpointv) whichcharacterizes a desired motor speed N is selected for control unit STE.The selection may, for example, be performed manually via apotentiometer. In this control unit STE, a function is stored whichreflects the dependence of PWM control signals PWM_(actual) forsemiconductor output stages EST on the associated setpoint speedN_(setpoint).

If a setpoint N_(setpointv) is selected and control unit STE andsemiconductor output stages EST are connected to supply voltage U_(batt)(i.e., switched on), then a selected acceleration of motor M to theintended setpoint speed N_(setpointr) is forced. For this purpose, aramp-type PWM control which effects an increase in speed using PWMcontrol signals PWM_(endr) is performed and this is done in a selectedor selectable acceleration time. In each phase of the acceleration, thesetpoint speed N_(setpointr) associated with the corresponding PWMcontrol signal is compared with a detected actual speed N_(actualr) by acomparison device VE in the control unit. Comparison device VE, whichmay be integrated into control unit STE, outputs a switch-off signal ABin the event a selected or selectable speed deviation ΔN is exceeded, inorder to switch off control unit STE and/or semiconductor output stagesEST, as contacts ab show, and to protect motor M and the electroniccomponents from overload. The comparison between the two values—setpointspeed N_(setpointr) and actual speed N_(actualr)—may be performedcontinuously or at intervals during the acceleration phase, with thepossibility always existing of switching off if permissible speeddeviation ΔN is exceeded.

The acceleration time may additionally be tailored to the magnitude ofselected setpoint N_(setpointv) and to the magnitude of supply voltageU_(batt), with, for example, the acceleration time of the ramp alsoincreasing with increasing setpoint N_(setpointv). Permissible speeddeviation ΔN may also be varied. Thus, permissible speed deviation ΔNmay also increase and be selected larger with increasing magnitude ofsetpoint N_(setpointv). The same also applies for supply voltageU_(batt).

For specific applications it may be advisable to evaluate the exceedingof permissible speed deviation ΔN in control unit STE, display itoptically and/or acoustically, and switch off control unit STE and/orsemiconductor output stages EST with a delay, which may still avoid anoverload of motor M and the electronic components.

The comparison between setpoint speed N_(setpointr) and actual speedN_(actualr) performed in the acceleration phase may also be performed inthe subsequent steady-state operation of motor M using the setpointspeed determined by selected setpoint N_(setpointv) and used foroverload protection.

What is claimed is:
 1. An electronically commutated motor comprising: acontrol unit; a plurality of semiconductor output stages; field windingscontrollable by the control unit via the plurality of semiconductoroutput stages using a plurality of PWM control signals, a nominalsetpoint speed being selectable for the control unit, an actual speedbeing comparable with the nominal setpoint speed, wherein in an event ofa deviation of the actual speed from the nominal setpoint speed by aselectable speed difference, at least one of the control unit and theplurality of semiconductor output stages is capable of being switchedoff; wherein with at least one of a selection of the nominal setpointspeed and a switching on of at least one of the control unit and theplurality of semiconductor output stages as a function of the nominalsetpoint speed, the control unit determines an acceleration time inwhich the plurality of PWM control signals increase the actual speedgradually to a final value associated with the nominal setpoint speed;wherein in the control unit, another setpoint speed is associated witheach control value of the plurality of PWM control signals; wherein ineach control phase of acceleration time, the actual speed is measuredand compared with the other setpoint speed associated with thecorresponding PWM control signal; and wherein a switching-off occursduring the acceleration time if in the control phase the actual speeddeviates from the other setpoint speed associated with the correspondingPWM control signal by the selectable speed difference.
 2. Theelectronically commutatable motor according to claim 1, wherein at leastone of an amplitude of a pulse, a pulse width, and a commutationfrequency of the plurality of PWM control signals continuously increasesduring the acceleration time.
 3. The electronically commutatable motoraccording to claim 1, wherein the actual speed and the other setpointspeed are compared during the acceleration time at least one ofcontinuously and repeatedly at a plurality of time intervals.
 4. Theelectronically commutatable motor according to claim 1, wherein at leastone of the control unit and the plurality of semiconductor output stagesis switched on and off by switching a voltage supply on and off.
 5. Theelectronically commutatable motor according to claim 1, wherein theacceleration time is dependent on a magnitude of a supply voltage. 6.The electronically commutatable motor according to claim 1, wherein theselectable speed difference is dependent on at least one of the nominalsetpoint speed and a magnitude of a supply voltage.
 7. Theelectronically commutatable motor according to claim 1, wherein theswitching off of at least one of the control unit and the plurality ofsemiconductor output stages is at least one of optically displayable andacoustically indicated.
 8. The electronically commutatable motoraccording to claim 1, wherein the comparison of the other setpoint speedand the actual speed is performed by a comparison device integrated inthe control unit.
 9. The electronically commutatable motor according toclaim 1, wherein the comparison between the other setpoint speed and theactual speed is continued with the nominal setpoint speed after theacceleration time for a duration of an operation of the electronicallycommutatable motor.